Angling for Thyroid Answers
Study Links PBDEs to Hormone Disruption in Male Sport-Fish Consumers
Levels of polybrominated diphenyl ethers (PBDEs) measured in human
samples have increased in recent years, but the health effects of these
compounds are not well studied. A group of persistent pollutants
similar in structure to polychlorinated biphenyls (PCBs), PBDEs are
thought to affect endocrine function, but this relationship has only
been examined in several small studies. A new study significantly
expands this knowledge base by analyzing PBDE exposure among a large
cohort of male sport-fish consumers and concluding that these exposures
are associated with increased thyroglobulin antibodies and increased
thyroxine (T4) in adult males independent of PCB exposure
EHP 116:1635–1641; Turyk et al.].
The study examined 405 adult males who consumed sport
fish from the Great Lakes during the early 1990s. Researchers gathered
data on the subjects' levels of fish consumption, medical diseases, and
use of medications, and took serum samples that were tested for PBDEs,
PCBs, and DDE, a metabolite of DDT that may affect thyroid hormones.
Total and free T4 and triiodothyronine (T3) were measured in serum and urine.
PBDE concentrations were positively associated with increased T4 and reverse T3, and inversely correlated with total T3 and thyroid-stimulating hormone (TSH). In addition, PBDEs were positively related to the percentage of T4 bound
to albumin, a carrier protein. An observed increase in thyroglobulin
antibodies in men with the highest PBDE exposures may indicate an
increased susceptibility to autoimmune thyroiditis among people who
have been exposed to PBDEs, according to the authors.
The findings of a positive association of PBDEs with T4 are not consistent with results of animal studies that have shown decreased T4 in
rats and mice exposed to PBDE. However, the results do align with those
of several smaller human studies. The authors speculate the disparity
may be attributable to the fact that, while thyroid hormone regulation
is similar among vertebrates, some functions differ by species.
A major strength of the study is the measurement of the effects of
PBDEs on multiple hormones and the consideration of other environmental
exposures that can affect thyroid hormones. The authors point out that
their findings provide a rationale for future mechanistic studies
related to PBDE exposure, including how those exposures may be linked
to changes in thyroid hormone metabolism and binding of T4
to serum-binding proteins. Also needed, they write, are larger studies
to determine whether PBDE exposure is related to thyroid disease in